Purpose: :
The dynamic distribution of proteins in tears has a vital rolein the maintenance of the ocular surface. However, little isknown about the PRPs of tear fluid although it is vastly distributedand has been proven as biomarker, which makes these proteinsinteresting candidates for in-depth proteomics analysis.

Results: :
A total of 70 unique proteins can be distinctly identified andan average of 10% of total proteins is PRPs based on the semiquantitative MS approach. Further characterization of tear proteinin 2nd DE showed a total of 12 spots related to PRPs with threedistinguished molecular weights of 19, 23 and 26 kDa, and pIvalues in the range between 5.5 to 3. Existence of wide polymorphismof PRPs reflect their post-translational modifications (PTMs),especially phosphorylation. Unique peptides from the PRPs richregion and all 12 spots identified from the 1st and 2nd DE,showed four distinguished types of peptide combinations from1601, 1729, 1792 & 1920 m/z for all samples analyzed individually.Sequencing results from tandem MS showed that all four peptidesare differentiated by the positions of Glutamine (Q) amino acid.Combinations of these peptides yield Proline Rich Protein 4(PROL4_HUMAN), pHL E1F1 (gi 1050983) and proline rich 4 (lacrimal)isoform 2 (gi 154448886) proteins from NCBI and SwissProt databasesby MASCOT (Matrix Science) search.

Conclusions: :
This work represents one of the most extensive proteome profilesof PRPs generated hitherto from tear fluids by taking advantageof the 2nd DE and MS approaches to identify the PRPs PTMs andclassify the PRPs into four different peptide combinations.The recurrence of these different types of PRPs in individualsand its potential as biomarkers for specific pathology is yetto be determined.